1. Technical Field
The present invention relates to a liquid-supplying system that is installed in a liquid-consuming apparatus including a reciprocating carriage having a head and supplies liquid to the head that consumes the liquid, and to the liquid-consuming apparatus. More particularly, the invention relates to a liquid-supplying system in which liquid reserved in a main tank is supplied to a head through a subtank mounted on a carriage, and to a liquid-consuming apparatus.
2. Related Art
An example of a liquid-consuming apparatus is an ink jet recording apparatus which prints images or the like using a recording head that ejects and applies fine ink droplets onto a recording paper, the recording head being mounted on a carriage reciprocating in a direction orthogonal to a direction in which a piece of recording paper is transported.
Such an ink jet recording apparatus is now used in various printing operations including color printing because it makes a relatively low noise during printing and is capable of forming fine dots at a high density.
For use in such an ink jet recording apparatus, various types of systems for supplying ink to a recording head have been proposed in which ink reserved in a main tank is supplied through a subtank mounted on a carriage.
In an ink-supplying system employing this method, a large amount of ink can be reserved in the main tank. Therefore, frequency of ink change due to ink exhaustion can be reduced and usability of the ink jet recording apparatus can be improved.
The recording head of an ink jet recording apparatus controls ejection of ink droplets by utilizing heat or vibration. If ink in an ink cartridge runs out and an ink-ejecting operation is performed in an inkless state, that is, blank ejection occurs, a malfunction may occur. Therefore, the ink jet recording head needs to be capable of monitoring the residual amount of ink in an ink-supplying system so as to prevent the recording head from performing blank ejection.
In an ink-supplying system in which ink reserved in a main tank is supplied to a recording head through a subtank provided on a carriage, the residual amount of ink is, in general, monitored by one of the following two common methods.
One method employs a sealed-container-type flexible ink pack as a main tank. In this method, ink in the ink pack is supplied to a subtank by applying a pressure to the ink pack and deformation of the ink pack caused by ink consumption is detected, whereby the residual amount of ink is monitored (refer to Japanese Unexamined Patent Application Publication No. 11-192720, for example).
The other method employs an ink reservoir that is opened to the atmosphere to be provided in a subtank mounted on a carriage. In this method, the residual amount of ink is monitored on the basis of the liquid level of ink reserved in the ink reservoir of the subtank (refer to Japanese Unexamined Patent Application Publication No. 11-123833, for example).
However, in the ink-supplying system in which a sealed-container-type flexible ink pack is employed as a main tank so that ink in the ink pack is supplied to the subtank by applying a pressure to the ink pack and the residual amount of ink is monitored by detecting deformation of the ink pack caused by ink consumption, it is problematic that a more complicated system configuration and a higher cost may be required for providing means for pressurizing the ink pack.
It is also problematic that variation in deformation of the ink pack caused by ink consumption may lower accuracy in detecting the residual amount of ink and make it difficult to precisely estimate the timing of ink change or the like on the basis of the residual amount of ink.
Moreover, the main tank cannot be refilled with ink during operation because the main tank has a sealed structure. Therefore, it is inconvenient that the degree of freedom in ink refilling is low.